1. Field of the Invention
The present invention is related to a directly motor-driven structure of a sewing machine, in which the driving motor is a high power motor with small volume and can directly drive the upper driving shaft to greatly reduce the noise and minify the vibration in operation. Moreover, the conventional fixing bracket for mounting the driving motor is omitted. Therefore, the structure and installation procedure are simplified.
2. Description of the Prior Art
FIGS. 1 and 2 show an existent sewing machine, especially an industrial sewing machine 40. The driving motor 41 is locked under the table board 43 by a fixing bracket 42. A belt wheel 44 is fixedly mounted on the rotary shaft of the driving motor 41. Sequentially through a belt 45 and a belt wheel 46, the belt wheel 44 drives the lower driving shaft 48 pivotally disposed in the lower section of the housing 47 of the sewing machine. A belt wheel 49 is fixedly mounted on the lower driving shaft 48. Through a belt 50 and a belt wheel 51 of the upper driving shaft 52, the belt wheel 49 drives the upper driving shaft 52 pivotally disposed in the upper section of the housing 47 of the sewing machine. Accordingly, the upper and lower driving shafts 52, 48 synchronously respectively drive the upper and lower stitching needles (not shown) to perform sewing operation. In order to reduce the vibration generated in operation of the sewing machine, the bottom face of the entire sewing machine 40 is locked on the upper face of the table board 43 by four bolts. However, the vibration can be hardly eliminated. Therefore, the sewing machine is simply xe2x80x9cplacedxe2x80x9d on four buffering pads 53 and can be hardly fir locked by the bolts. Such structure has some shortcomings in use as follows:
1. The transmission distance of the belt 45 is too long. In the case that the belt 45 is over-tensioned, in operation, the sewing machine will vibrate to make a noise.
2. In the case that the belt 45 is over-tensioned, when the belt 45 is revolved on the upper and lower belt wheels 46, 44, a noise will be produced.
3. The driving motor 41 has a large volume and heavy weight and must be locked on the table board 43 of the sewing machine by the fixing bracket 42. Therefore, the sewing machine has a quite large volume and heavy weight and cannot be easily transferred.
4. The driving motor 41 is exposed to outer side of the sewing machine and not shaded. Therefore, the driving motor 41 tends to be contaminated by dust. Moreover, the belt 45 revolves on outer side of the sewing machine and is likely to tangle with alien article or even hurt a user""s fingers.
Many kinds of improved motors with small volume and great torque have been developed. In the case that such driving motor is directly mounted on the sewing machine and the driving shaft of the motor is directly drivingly coupled with any rotary shaft of the sewing machine, the noise produced in transmission can be greatly reduced. In addition, the installation can be facilitated. However, it is necessary to consider the following problem:
Referring to FIG. 2, many transmission members are disposed on left side of the belt wheel 46 so that the belt wheel 46 cannot be retracted inward, that is, retracted leftward according to FIG. 2. Besides, the upper and lower belt wheels 51, 49 must be mounted in the housing 47 of the sewing machine 40 in alignment with each other. In the case that the driving motor 41 is mounted in lower section of the housing 47, that is, mounted at right end of the lower driving shaft 48, the driving motor 41 will protrude outward from right end of the housing 47. As a result, the gravity center of the driving motor will suspend outside the housing 47. Therefore, after the driving motor is added to the sewing machine, the gravity center of the entire sewing machine will moved rightward. Accordingly, when operating, the sewing machine is likely to vibrate and produce noise.
It is therefore a primary object of the present invention to provide a directly motor-driven structure of a sewing machine. The sewing machine includes: an upper driving shaft mounted on upper side of a housing of the sewing machine for driving an upper stitching needle; a lower driving shaft mounted on lower side of the housing for driving a lower stitching needle; and a driving motor for driving the upper and lower driving shafts, making the upper and lower stitching needles perform sewing operation. The directly motor-driven structure includes: a middle rotary shaft pivotally mounted in a middle section of the housing between the upper and lower driving shafts; a first transmission mechanism connected between the lower driving shaft and the middle rotary shaft to drivingly rotatably connect the lower driving shaft with the middle rotary shaft, the first transmission mechanism being spaced from the lower stitching needle by a first length; and a second transmission mechanism connected between the upper driving shaft and the middle rotary shaft to drivingly rotatably connect the upper driving shaft with the middle rotary shaft. The second transmission mechanism is spaced from the upper stitching needle by a second length. The second length is smaller than the first length, whereby the sewing machine is formed with a recessed installation space adjacent to the second transmission mechanism. The driving motor is installed in the recessed installation space and directly fixedly connected with the upper driving shaft so as to reduce the noise in transmission. The total volume of the sewing machine is reduced. Moreover, the conventional fixing bracket for mounting the driving motor under the table board is omitted. Therefore, the structure and installation procedure are simplified.
The present invention can be best understood through the following description and accompanying drawings wherein: